Field of the Invention
The present invention relates to an electric storage cell comprising an electric storage element sealed by a covering film, to a covering film, and also to an electric storage module comprising a stack of such electric storage cells.
Description of the Related Art
Film-covered electric storage cells, each comprising an electric storage element sealed by a covering film, are widely used in recent years. Film-covered electric storage cells are subject to rising pressure in the electric storage cell due to generation of gaseous species as a result of electrolysis of the electrolytic medium during use, if the control circuit of the electric storage cell fails for some reason and abnormal voltage is applied or the ambient temperature rises to an abnormally high level for some reason. As the internal pressure of the film-covered electric storage cell rises, eventually its covering material ruptures and gas erupts from the ruptured location; since it is impossible to predict where the covering material will rupture, however, the surrounding equipment, etc., may be negatively affected depending on the ruptured location.
To solve this problem, Patent Literature 1, for example, discloses a constitution where a peninsula-shaped projecting fusion part is provided in the seal part of the covering film and a through hole is formed in the projecting fusion part in order to release the pressure in case the covering film expands and its separation progresses. This way, the tear-off stress generated by the expansion of the film can be concentrated to the projecting fusion part to facilitate the progression of separation, so that the pressure is easily released as the film expands.
Background Art Literatures
Japanese Patent Laid-open No. 2005-203262